Hmmmm... Have a look to https://app.originstamp.org/homeLet us call it "close timestamps" contrary to "open timestamps" I think it is not very hard to compare these two projects and understand the technique.If no, you must give up and switch to something else.

I'm guessing that they create an unspendable output with an OP_RETURN which allows you to embed arbitrary data in a transaction. So, they can aggregate a bunch of individual hashes into a single hash, then submit a Bitcoin transaction to an unspendable output with OP_RETURN that contains the literal bytes of the aggregated hash. So, for the cost of about 70-80 bytes or so (assuming compressed signatures), you can embed an unbounded number of hashes into a Bitcoin block, thus timestamping all of those hashes with that block.